ZyXEL P-2812HNU-51c User Manual download pdf (Page 129)

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Chapter 5 WAN Setup

P-2812HNU-51c User’s Guide

129

Full Cone NAT

In full cone NAT, the NAT router maps all outgoing packets from an internal IP

address and port to a single IP address and port on the external network. The NAT

router also maps packets coming to that external IP address and port to the

internal IP address and port.

In the following example, the P-2812HNU-51c maps the source address of all

packets sent from the internal IP address 1 and port A to IP address 2 and port B

on the external network. The P-2812HNU-51c also performs NAT on all incoming

packets sent to IP address 2 and port B and forwards them to IP address 1, port

Figure 52 Full Cone NAT Example

Restricted Cone NAT

As in full cone NAT, a restricted cone NAT router maps all outgoing packets from

an internal IP address and port to a single IP address and port on the external

network. In the following example, the NAT router maps the source address of all

packets sent from internal IP address 1 and port A to IP address 2 and port B on

the external network.

The difference from full cone NAT is in how the restricted cone NAT router handles

packets coming in from the external network. A host on the external network (IP

address 3 or IP address 4 for example) can only send packets to the internal host

if the internal host has already sent a packet to the external host’s IP address.

A server with IP address 1 and port A sends packets to IP address 4. The P-

2812HNU-51c changes the server’s IP address to 2 and port to B.

Both 4, D and 4, E can send packets to 2, B since 1, A has already sent packets

to 4. The P-2812HNU-51c will perform NAT on the packets from 4, D and 4, E and

2, B

1, A

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